The present invention relates to an improved peristaltic pump and method of pumping fluids. In particular, the invention is directed to a new peristaltic pump and method useful for drug infusion.
In the past, peristaltic pumps have generally been formed with a housing member defining an arcuate surface less than 360.degree. and a resilient tubing provided in the inner radial periphery of the housing. A rotatable member having pressure elements or rollers engages the resilient tubing at spaced apart points and compresses the tubing. As the pressure elements move along the tubing, a liquid is drawn from a suction end and supplied under pressure to a discharge or supply end.
Such known peristaltic pumps present two major problems to their miniaturization and usefulness as ambulatory or implantable drug infusion devices. One of these problems is the backflow of pumped fluid due to the recovery of the peristaltic tube at its discharge end when the compressing cam or roller leaves the tube and proceeds to compress the tube at the suction end. The second problem is the high torque associated with compressing the peristaltic tube which is generally an elastomeric tube having a round cross section.
An object of the present invention is to provide an improved peristaltic pump which avoids the aforementioned problems or disadvantages associated with the known pumps so that it can be made relatively small and used as an ambulatory or implantable drug infusion device.
More specifically, an object of the present invention is to provide an improved peristaltic pump wherein the above-discussed backflow problem is overcome such that the flow discharge rate from the pump remains positive and almost constant during operation, and wherein the force associated with compressing a peristaltic tube can be minimized so that a relatively low torque is required to drive the pump.
An additional object of the invention is to provide an improved peristaltic pump having high integrity and reliability and which is characterized by a lumen which is free from undesirable creep and distortion.
These and other objects of the present invention are attained by providing a peristaltic pump comprising at least one peristaltic tube means defining a lumen extending from a suction end to a discharge end of the tube means, and an at least essentially planar, spiral cam engaging the tube means and closing the lumen thereof with at least one of the spiral cam and the tube means being rotatable relative to the other to effect pumping. This arrangement permits the pump to be relatively lightweight and compact.
In a disclosed, preferred embodiment of the invention the pump comprises a plurality of peristaltic tube means with the spiral cam engaging each of the tube means and closing the lumens thereof at a minimum of one point, and preferably two points, during the operation of the pump. According to the invention, the plurality of peristaltic tube means are formed integrally with one another by molding so as to minimize creep and distortion thereof.
More particularly, in the disclosed embodiment of the invention the peristaltic pump is formed with three peristaltic tube means whose suction ends are in fluid communication with a common suction port and whose discharge ends are in fluid communication with a common discharge chamber. The peristaltic tube means extend radially outwardly from the common suction port at equal angular spacings of 120.degree..
A round support member is provided for supporting the spiral cam of the pump. The support member and cam thereon are rotatable with respect to the peristaltic tube means of the pump. As an additional feature of the invention, a plurality of bearing means are provided at spaced intervals about the outer circumference of the round support member for guiding and positioning the support member and cam during rotation. Means are provided for adjusting the position of the bearing means to control the position of the support member and the spiral cam thereon with respect to the peristaltic tube means during operation of the pump. This arrangement permits an accurate adjustment of the pressure placed on the peristaltic tube means by the cam so that the tube means can be closed to prevent fluid bypassing under pressure without the application of excessive pressure which has a negative effect on required driving force and energy consumption of the device.
Further, according to the invention the cross sections of the open lumens defined by the peristaltic tube means are identical segments of a circle. Such a structure reduces the stress induced in the tube means and minimizes the compressive load needed to close the lumen thereof as compared with an elastomeric tube of round cross section. This in turn reduces the friction and the torque required to drive the device. Therefore, a smaller motor and batteries can be used with the pump thereby resulting in less weight and size.
As another feature of the invention, the end of the spiral cam which contacts the tube means adjacent the discharge end thereof during operation is extended as a cam portion having an essentially uniform radius of curvature and a height which gradually decreases so that the recovery of a peristaltic tube means adjacent the discharge end is gradual thereby minimizing the flow rate drop associated with such recovery. During this recovery all peristaltic tube means of the pump continue to deliver or discharge fluid so that the overall flow rate of the pump to the common discharge chamber remains positive and almost constant. Specifically, with an arrangement according to the disclosed, preferred embodiment having three peristaltic tube means spaced at regular intervals of 120.degree., the flow rate drop is inherently divided by two thirds as compared to a single peristaltic tube device.
The method of peristaltically pumping a fluid according to the invention comprises the steps of providing a source of fluid to be pumped, providing a plurality of peristaltic tube means each defining a lumen extending from a suction end in fluid communication with the source to a discharge end in fluid communication with a common discharge chamber, compressing each of the tube means at at least one point along the length thereof to close its lumen and progressively advancing the points of closure of each lumen in the direction of the discharge end of the tube means to pump fluid from the source through each of the tube means to the common discharge chamber. The moving points of closure of the lumens are at different relative positions along the lengths of the respective tube means so that the fluid discharges from the discharge ends of the tube means are out of phase with one another.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, one preferred embodiment in accordance with the present invention.